docs: def get_previous_instance(self, obj):
          """
          Return the previous plugin instance for the given object.
          This differs from `obj.get_prev_sibling()` which returns an unsorted sibling.
          """
          ordered_siblings = obj.get_siblings().filter(placeholder=obj.placeholder).order_by('position')
          pos = list(ordered_siblings).index(obj.cmsplugin_ptr)
          if pos > 0:
              prev_sibling = ordered_siblings[pos - 1]
              return prev_sibling.get_bound_plugin()